Sunderland boss on Bryan Oviedo's absence and why Tom Flanagan dropped to the bench at Oxford
The Costa Rican has not been involved in either of the matchday squads since his deadline day switch to West Brom fell through at the last minute.
Jack Ross has preferred Reece James in league action for a number of games now, though the team's indifferent form has led for some to call for the experienced international to return.
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Hide AdBut after picking up an injury in training last Thursday, Oviedo remains sidelined for the time being.
"He was injured [on Saturday] and still injured," Ross said.
"He's got a sore calf."
Denver Hume, a likely challenger for the left-back role, is expected to play again in the U23 side on Monday night as he nears full fitness.
One defensive change that could happen on Tuesday night is the return of Tom Flanagan.
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Hide AdThe Northern Ireland international has been a mainstay of the side under Ross but dropped to the bench at the Kassam Stadium.
Ross explained that his partner had given birth last week.
"Tom's partner had a baby last week so we didn't have him in until late in the week," he said.
"He didn't train at all until Thursday."
Lee Cattermole could return to the squad after recovering from an ankle problem while Ross also confirmed that Glenn Loovens is fit again.
The experienced defender has not been part of a matchday squad since being sent off in the 3-1 defeat to Portsmouth just before Christmas.
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Hide AdThe arrival of Jimmy Dunne in January has pushed Loovens further down the pecking order.
"Glenn has been back for two or three weeks now," Ross said.
"The reality is we have a lot of options now.
"But his influence off the pitch and around the training ground is good. He's been a benefit from day one, we needed that and we we'll continue to need it over the coming months."